1227747 to 16197427 Conversion PCM Swap with Wiring Pinout Directions!

[CDeeZ]

Chris how did you find this website?!?! That's it, Fast has made his arrival, time to shut the forum down! LOL JK man, glad to have you on here with your EFI-veteran status!



I agree on trying to eliminate the confusion on the knock sensor wiring when upgrading from the 747 ECM to the 7427 PCM, I went through the same thing myself. Blue to brown gives you two grounds on some GM vehicles (which obviously won't work b/c that's only half of the circuit). The multimeter is the only surefire way. It also doesn't help that the wire colors underhood are further obscured by fading/grime accumulation.


Also, I'm not as learned as some of the guys on here, but I have to agree, with what little I know, that the 7427 does indeed have better cold start routines, and also is just better all around in my opinion. Perhaps part of this is the additional resolution on things like fuel tables?

[dave w]

I think this is a good tread to post a budget update about converting a vehicle with the 1227747 / TH400 combination to a 16197427 PCM which does not have a TH400 Kick Down control.

On vehicles with a 1227747 the TH400 Kick Down Relay is controlled by ECM pin A7 (tan wire with a black stripe), which sends a ground to the Kick Down Relay. The simple budget fix is to install a TH400 Kick Down Switch on the Accelerator Pedal, just like the older non-computer controlled GM Pickups used. The HUGE difference is ECM pin A7 will be switched to ground (black wire with a white stripe) through the Kick Down Switch to make the TH400 Kick Down Relay work. One side of the Accelerator Pedal Mounted Kick Down Switch will be connected to ground and the other terminal of the Accelerator Pedal Mounted Kick Down Switch will be connected to pin A7.

For a long term trouble free service, solder splicing the wiring is HIGHLY RECOMMENDED!

The pictures below are from a 1987 C3500 454 / TH400 that has been updated to a 16197427 PCM that is using an Accelerator Pedal Mounted TH400 Kick Down Switch. The older Accelerator Mounted TH400 Kick Down Switch is a direct bolt in, no modifications required.

dave w

[Fast355]

I think this is a good tread to post a budget update about converting a vehicle with the 1227747 / TH400 combination to a 16197427 PCM which does not have a TH400 Kick Down control.

On vehicles with a 1227747 the TH400 Kick Down Relay is controlled by ECM pin A7 (tan wire with a black stripe), which sends a ground to the Kick Down Relay. The simple budget fix is to install a TH400 Kick Down Switch on the Accelerator Pedal, just like the older non-computer controlled GM Pickups used. The HUGE difference is ECM pin A7 will be switched to ground (black wire with a white stripe) through the Kick Down Switch to make the TH400 Kick Down Relay work. One side of the Accelerator Pedal Mounted Kick Down Switch will be connected to ground and the other terminal of the Accelerator Pedal Mounted Kick Down Switch will be connected to pin A7.

For a long term trouble free service, solder splicing the wiring is HIGHLY RECOMMENDED!

The pictures below are from a 1987 C3500 454 / TH400 that has been updated to a 16197427 PCM that is using an Accelerator Pedal Mounted TH400 Kick Down Switch. The older Accelerator Mounted TH400 Kick Down Switch is a direct bolt in, no modifications required.

dave w

Dave,

Interesting idea however I am thinking a small patch could be added to control the downshifts similarly to the shift light logic. No extra hardware created.

[dave w]

Dave,

Interesting idea however I am thinking a small patch could be added to control the downshifts similarly to the shift light logic. No extra hardware created.

I agree, a small patch would be a good option.

dave w